A decacyclic indacenodithiophene-based non-fullerene electron acceptor with meta-alkyl-phenyl substitutions for polymer solar cells†
Indacenodithiophene (IDT) is a promising building block for designing organic semiconductors. In this work, a new decacyclic building block (m-IDTIDT) with a double IDT unit and meta-alkyl-phenyl substitutions was synthesized and used for designing a new non-fullerene electron acceptor (m-IDTIDT-FIC). Compared to p-IDTIDT-IC, m-IDTIDT-FIC has a smaller π–π distance, larger crystalline coherence length, and higher electron mobility. Thus, polymer solar cells (PSCs) based on PCE10:m-IDTIDT-FIC can achieve a higher PCE (8.27%) than PCE10:p-IDTIDT-IC-based PSCs (6.48%). In addition, PSCs based on J71:m-IDTIDT-FIC show better photovoltaic performances than PSCs based on PCE10:m-IDTIDT-FIC. This is because the J71:m-IDTIDT-FIC blend film has more balanced charge transport ability, a smooth surface, and higher relative domain purity than the PCE10:m-IDTIDT-FIC blend film. PSCs based on J71:m-IDTIDT-FIC exhibited the best photovoltaic performances with a PCE of 11.32%, an open-circuit voltage (Voc) of 0.92 V, a short-circuit current (Jsc) of 18.01 mA cm−2, and a fill factor (FF) of 68.30%. These results indicate that m-IDTIDT with meta-alkyl-phenyl substitutions is a promising IDT-based building block for high-performance non-fullerene electron acceptors.